tools/check: skip 'tests' directory in 'make ut' (#35800)
tools/check: skip 'tests' directory in 'make ut' (#35800)

close pingcap/tidb#35799
ngaut/tidb,pingcap/tidb,kyle-wang/tidb,pingcap/tidb,ngaut/tidb,kyle-wang/tidb,ngaut/tidb,ngaut/tidb,kyle-wang/tidb,pingcap/tidb,pingcap/tidb,pingcap/tidb,kyle-wang/tidb,ngaut/tidb,kyle-wang/tidb,ngaut/tidb,pingcap/tidb,kyle-wang/tidb